


i'm a sucker for sans x gaster fluff

by rag__tag



Category: Undertale (Video Game)
Genre: #qvvarstillcantdotitles2k16, Fluff, M/M, Post pacifist, Sanster, gaster is NOT dadster, gaster x sans, i was honestly really bored and wanted to write some sanster fluff, maybe a few spoilers? idfk, w.d. gaster x sans
Language: English
Status: Completed
Published: 2016-07-04
Updated: 2016-07-04
Packaged: 2018-07-20 01:29:09
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 3,658
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7385515
Author URL: https://archiveofourown.org/users/rag__tag/pseuds/rag__tag
Summary: <blockquote class="userstuff">
              <p>Sans and Gaster have been dating for a month or so, and Sans is craving to spend more out of work time with Gaster.<br/>This is post-pacifist because I wanna see all the dorks be happy, too :')</p>
            </blockquote>





	1. what are chapter titles :'|

**Author's Note:**

> As you guys know, I still can't do good titles :|  
> whelp, I was surprised by how many people liked my Sans and Paps one, so I decided to do some Sanster fluff because THE WORLD NEEDS IT.  
> anyway.. i hope you guys enjoy it!! it's supposed to be a one shot but ended up being too long, so i'm uploading it in 2 chapters

It was just another normal day in the lab. Most of the workers were helping Gaster with his current project: some sort of strange piece of machinery that allowed monsters and humans of all kinds to have the ability to travel to different universes and back. Gaster had only returned from the void six months before this very day, and he absolutely loved the surface. There were so many different interesting scientific concepts that the humans had, and he wanted to learn about every single one of them.  
For this day, most of the work that had to be done was paperwork, and there wasn’t very much hands-on, practical work needed to be done for this current week. All of the workers were a little bored with it, but they knew that the more they worked on it, the quicker it’d be up and out with. However, a worker in particular, was boreder than the others. He was less willing to work than the others, as well. That worker was Sans.   
Gaster and Sans had an extremely close friendship over the years, and they still did this very day. He always seemed to enjoy the puns that Sans would tell, which meant a lot to the smaller skeleton. Normally, on most days, Sans would be extremely happy to work in the lab, and he normally seemed happier than most of the other workers. Gaster always wondered why, maybe Sans was a lot more passionate about science than he ever imagined? Or maybe there was some spark in him? Or… maybe it was someone’s presence that made him happy? Nevertheless, Gaster was always put in a good mood when he saw Sans’s happy and enthusiastic attitude towards working in the laboratory with him.

It was 8:30AM, a time that the workers would normally come in at. They’d normally come in half an hour earlier than the actual starting time to prepare the things they needed for work that day. Sans, however, always came in at 8:55AM, being the loveable lazybones that he always was. But today, he didn’t come in until 9:05. Gaster wasn’t worried by this, as Sans tended to be late quite often. As Sans walked in the door, Gaster looked over and smiled.  
“Good morning, Sans. Did you sleep in a bit?”  
“yeah, i guess.” Sans lied. Really, he had spent most of the morning feeling drained. He wasn’t feeling depressed, but he felt tired. He just wanted to snuggle up in a warm bed, and sleep for as long as he wished to. At that very moment, he forgot why he was even feeling physically and mentally drained in the first place. He had gotten a good night’s sleep. He shrugged it off, and walked to his normal workspace, next to where Gaster normally worked at. Gaster also walked to his workplace, and sat down. Sans sat down as well, and spoke.  
“so, uh… what work do we have to do today?”  
“Just paperwork, unfortunately. Don’t worry, tomorrow’s Friday, the final day of the working week.”  
“ah right.” All of the monsters in the lab got to work on what was left for them.  
Sans looked up at a clock. It was only 9:45AM. The time was dragging on slowly. He read through the miscellaneous pieces of paper that he worked through within the last fifteen minutes, correcting any mistakes that he would have made. He really wasn’t feeling up to working. He began to space out after correcting the last mistake on one of the papers, just thinking. Thinking about why he was so god damn sluggish that morning.  
He thought about how he wasn’t normally like this, especially when he had Gaster’s company. They both had such a close friendship, it’d be extremely hard to tear them apart. It’d take more than the power of every single person on the planet combined. He then began to think about how much of a wonderful monster Gaster was, and how nice he would always be for Sans. And it clearly wasn’t just an act. He wondered why Gaster was so fond for him. Then, he realised that he was also extremely fond for Gaster himself. Like the time when Gaster slipped on some substance in the lab a week ago, and Sans had rushed over to help him up. Sans couldn’t help but smile when he remembered how grateful Gaster was. And how adorable it was when Gaster held his hand to get up…  
Sans just remembered why he was so sluggish this morning. He remembered that he had actually ended up asking Gaster out two months ago. They hadn’t actually had many dates, because of being extremely busy in the lab. He just wanted to get closer and a little more intimate with Gaster. He just wanted to spend more time with him. A lot more time, in fact. Sans couldn’t help but just think about how nice it would be to regularly spend time with the scientist out of work. He didn’t realise that he was slipping away, daydreaming, until…  
“Sans?” Sans jolted when he heard Gaster’s somewhat whispery, calm voice say his name. Blue magic rushed up to his face, making him blush a little when he noticed how close Gaster was.   
“You were daydreaming.” Gaster giggled a little over how sudden Sans was to react.   
“i- uh- i’m sorry, i.. i guess i got a little carried away there, heh..” Sans nervously chuckled.  
“It’s fine. Have you finished this part of the work?”  
“n-no.. i’ll finish it off now!” Gaster nodded, and got back to his work. Sans looked up at the clock again. /shit. it’s already 10:25. how long have i been daydreaming for?/  
Sans had carefully gone through the paperwork, making sure there weren’t many mistakes. He looked over to his left, and saw Gaster. He suddenly felt this warm feeling in his chest and face, gazing at the other scientist. He snapped himself out of it, and spoke nervously.  
“uh.. doc—ah, gaster.. i finished it and i can’t find anything else that n—“  
“What about the other files there?” Sans looked.   
“oh, right. sorry.”  
“Don’t be.” Gaster replied reassuringly. He was close to adding, ‘I noticed you gazing at me, anyway.’ in a lighthearted manner, but he didn’t want to distract Sans too much from his work.  
It was 12:00PM. Finally time for a half an hour break. Sans got up from his seat, stretching, and groaning in relief. He noticed that Gaster hadn’t left, but everyone else had. He looked over, and felt that it’d be nice to give the scientist a friendly smile.   
“hey, aren’t you gonna go to the kitchen with everyone else?”  
“No, I’ll wait for you, Sans.”  
“aww, thanks.” Sans finished stretching, and he took his reading glasses off, placing them on the desk. The two skeletons walked out of the room, and into the kitchen. As they walked, Gaster spoke.   
“Hey, Sans, I’ve noticed you’ve been a bit… off. You haven’t told any puns today, much to my surprise. Is everything alright?”  
“yeah, everything’s fine… i think..? i’m just really tired, i dunno why. surprisingly, i even got a good night’s sleep last night, and yet i’m still tired?”  
“Is there anything that has been on your mind lately?”  
“um…” Sans began to blush again, looking away. No matter how hard he tried, he wouldn’t be able to hide his blush. Gaster couldn’t help but smile when he saw the light shade of blue dust the other skeleton’s cheeks.   
“i’d rather talk about that out of work.” Gaster nodded, and thought to himself for a bit. He then realised that he wasn’t busy after work on Friday, and he spoke.   
“Sans, can I ask you something?”  
“go ahead, g.”  
“Are you busy after work on Friday?”  
“nah. you?”  
“No, I’m not. Would you like to come over to my place to... I don’t know, just to hang out for a bit I guess? And have dinner as well? And maybe a movie or two?” Sans froze, and then looked up at Gaster, an unstoppable grin spreading on his face.   
“really? i’d absolutely love to! what time?”  
“Whatever suits you best.”  
“hmmm.. six?”  
“Sure. I noticed that you may have not been too well, and that you might like the idea of staying with me for a bit.”  
“i don’t just like the idea, i love—wait, wait..” Sans blushed.   
“i mean.. yeah, it’s a great idea!” Gaster giggled.  
The rest of the day flew, compared to how the morning went by. Sans didn’t want to leave when Gaster dismissed everyone. He stayed in a bit and had a conversation with the other scientist for a bit before he went home.  
Much to his surprise, Papyrus wasn’t upset about Sans coming back late. Sans kicked his shoes off, and got into some more comfortable clothes. They were both sitting in the living area, talking. Suddenly, Sans remembered the plan he had for tomorrow night.   
“hey, papyrus, i forgot to tell you. i’m staying over at gaster’s place tomorrow night, leaving at 6.”  
“GASTER?”  
“my boss.”  
“OH, THAT’S RIGHT. I SEEM TO FORGET HIS NAME FROM TIME TO TIME, ESPECIALLY WITH ALL OF THIS CARRY ON OF BEING ON THE SURFACE.” Sans chuckled a little. Papyrus was right, he too occasionally got carried away with the things he could do on the surface. The evening also flew by, and he was in bed before he knew it. He couldn’t get over how excited he was to be spending most, or maybe even all of the next night with Gaster.


	2. what are chapter titles :'| 2: electric boogaloo

The next day arrived. Sans woke up, feeling a lot brighter and happier than he was the previous day. He basically jumped out of bed, and walked out into the kitchen. It was 7:30AM. Papyrus looked over, and smiled.   
“SANS! YOU’RE UP EARLY!”  
“yeah. how are you?”  
“DOING EXCELLENT, AS ALWAYS. YOU?”  
“i’m actually really excited. being able to spend some out-of-work time with my boss.” Sans realised that he forgot to tell Papyrus that he was dating Gaster. He was 2 months late. Wow. He shook it off, thinking that it’d be funny to leave his younger brother a little confused for now. He eagerly ate his breakfast, had a shower and got dressed. It was only 8:25AM, and Papyrus was leaving to go to somewhere with Undyne. He didn’t know why Papyrus was going so early, but what he DID know was that he was going to be gone all day, and wouldn’t come back until very late that night, maybe even Saturday morning. Whelp, that was a relief for Sans. Sans decided to leave for work, and he walked all the way instead of taking a shortcut. He checked his watch that he finally decided to wear. 8:45AM. Earlier than normal! He knocked on the door, and the door was opened to reveal Gaster. He smiled at Sans.   
“You’re here earlier than normal!”  
“yeah. i’m actually really excited about tonight. i woke up at seven thirty instead of eight thirty, too.” Gaster smiled a little more widely, and let Sans in. Sans couldn’t help but gaze into Gaster’s eyes until they were out of his sight. He felt blessed to be able to work with someone as amazing as Gaster.  
The morning flew fast. He was getting a lot of work done, enthusiastic and determined about getting it all up and out with while still being efficient, knowing that the more work he did, the closer 6:00PM would come along. Sans was honestly impressed by how much work he was getting done. Even when his boss double checked it, he was also impressed by how accurate the information was. Gaster could tell that Sans was getting more and more excited by every minute.  
It was time for the lunch break, and everyone was in the kitchen. Sans couldn’t help but lovingly look up at Gaster while he ate, and Gaster noticed him every time. It was the 6th time that Sans was admiring him, and Gaster spoke.   
“I know you’re admiring me.” Sans blushed, and one of the other workers chuckled.   
“sorry, g. getting a little carried away. i don’t mean to be stalker-ish in any way..”  
“It’s fine. I’m excited for tonight, too.” Sans couldn’t describe how relieved he felt that Gaster was feeling the same way. Maybe Gaster’s feeling of excitement wasn’t as strong at Sans, but whatever it was, they were both definitely looking forward to seeing eachother out of work.  
It was already 3:30PM. Work would be finished for the week in half an hour. He began to slack off a little on his work, but in the end, he didn’t actually have a lot of paperwork left to finish at all. He spend the final 30 minutes finishing anything off and double checking any information, trying to keep his attention on the work, and not on Gaster and the little hang out they were going to have. Well, it could also be considered as a date. When he finished going over the papers, there was another ten minutes left. He began to think about what he should wear on the date. Maybe he could wear something different from his trademark blue hoodie, sports shorts and pink slippers. He would have to have a look in his closet when he got home. And he then began to wonder what he and Gaster would have for dinner, and what movie they’d watch together. Suddenly, he realised that everyone was beginning to pack up their work. He hurried to pack his equipment and papers up, and noticed that Gaster was sitting there, looking into the distance.   
“hey, g, what’s up?”  
“Oh, Sans! I’m just thinking… Thinking about the date tonight…”  
“funny you say that, because i was, too.” They both smiled. Gaster looked at the clock, and spoke.   
“Everyone, you can go home now. Have a good weekend.” Everyone said their goodbyes for the week, and Sans stayed there.   
“hey, g, where do you live?”  
“I live near this large town near Mount Ebbott. You?”   
“next door to where toriel lives.”  
“Oh, I know that place. Is your house the one with the red roof?”  
“yup.”  
“I’ve been past there several times.” Sans looked at the clock as well, and spoke.   
“well, i’m gonna go home and get some things organised. can you send me a text saying where your address is?”  
“Sure thing. I’ll see you at six, Sans.” Sans blushed when he heard Gaster say his name in a somewhat dreamy manner. He felt Gaster hold his hand and give it a gentle squeeze before he walked out. Sans blushed harder from the sudden sign of physical affection. He grinned, and walked out the door behind Gaster, turning the lights off as he went out the door.  
When Sans got home, he did the same as he did the previous day. He kicked off his shoes by the front door, and placed his bag on the floor next to the couch temporarily. Papyrus wasn’t home. He checked the time on his phone, it was now 4:40PM. Sans wanted to buy Gaster a gift, and there was plenty of time to grab one. He went down to a novelty store, and ended up going back home with a mug that said “I am made of NaCl, fluorine, iodine and neon, because I am sodium FINe.” Sans obviously fell in love with this mug when he saw it, and had to get it.  
When he returned home again, he went looking through his closet for something that was nice, but comfortable too. He ended up settling on a pair of black pants, some comfortable shoes and a decent looking jumper that had a blue and white checker pattern on it. It was still the sort of colors Sans would wear, but the actual pieces of clothing were clean and decent. He decided to go and check the text that Gaster sent him, and thought to himself. /dang. i should head off shortly./ He decided to get a few extra things, packed them into a smaller bag and he headed off, locking the door and placing the keys under the doormat. He set off, and arrived at Gaster’s house five minutes early. He knocked on the door, and Gaster came to answer it. 

“Sans, you’re early! Come on in.” Sans smiled, and kicked his shoes off at the front door, as he normally does.   
“hey, g, can you show me around this place?”  
“Of course, love.” Sans blushed at the nickname he was given, and he noticed that Gaster had his hand out, as a signal for Sans to hold it. They held hands as Gaster lead him around the house, also talking him through it. They both ended in the living area, having a conversation.   
“You look nice, Sans. Nice to see you in something like this.”  
“thanks. i tried for once.” They both giggled. He was expecting to see Gaster in what he normally wears to work, but instead, he was wearing a dark, pastel purple jumper and black pants, which Sans didn’t expect at all.   
“you look nice as well, g. in fact, you always look nice in anything.” Gaster smiled and blushed at the compliment he received.   
“So, I ended up starting on dinner earlier, getting it ready to be cooked. Do you fancy pizza?” Sans’s eyes lit up at that magical word. Pizza.   
“heck yeah!” Gaster lightly laughed at Sans’s reaction to what he had prepared.   
“Do you like hawaiian?”  
“i don’t care. pizza is pizza.” The taller skeleton nodded, taking out the pre-prepared pizza, and placing it in the oven, letting it cook. As it cooked, they both sat down in the small yet cute dining area, talking.   
“so… any plans for the weekend?”  
“Not really. You?”  
“nope. aside from sleeping.” Gaster smiled and nodded.   
“This week has been a pretty full-on paperwork week, it’d be nice to just cut loose and relax.” Sans nodded in agreement. Sans didn’t speak, and admired Gaster’s face for a bit. He suddenly remembered the gift, and spoke.   
“i’ll be right back. just gotta grab something.” Gaster patiently waited for Sans, and then smiled in surprise as he saw him return with a mug in his hands.   
“it’s for you.”  
“How thoughtful of you… Thank you, Sans.” Gaster had a look at it, and suddenly let out a somewhat hearty chuckle when he read the pun on it.   
“I love it! I’m definitely using this.”  
“i knew you’d like it. and, i mean, you are! you really are made of sodium, fluorine, iodine and neon.” Sans grinned proudly, and earned another chuckle from Gaster.   
“Sans, I think you’re starting to work yourself down to the bone again.”  
“nah, i can work a lot harder than this tibia honest.”  
“These puns are starting to become hard to hand-le.”  
“alright, let’s stop. if you keep on saying these puns, i’m gonna start skull-king, because i won’t have any more puns to be able to tell you.” They were silent for a moment, and both chuckled.   
“that was amazing.”  
“I know! We should do that more often.” They both smiled, and Gaster sighed, looking into Sans’s eyes. This caused Sans’s cheeks to be dusted with a faint shade of blue. Sans smiled, and went to hold Gaster’s hand, looking into the taller skeleton’s eyes in return. Suddenly, Gaster shot up.   
“The pizza!” He looked in the oven.   
“It’s almost ready.” Sans nodded, ignoring what he was saying, and just admiring him.  
A few minutes later, Gaster took the pizza out, and they began to eat. Sans’s eyes widened, and he spoke.   
“this is amazing! how do you manage to cook so well?”  
“Took years of practice. When I started out, well… It was pretty ugly. I’d burn the whole kitchen.”  
“sounds like papyrus and his spaghetti.” They both chuckled.   
“he’s getting better at it though, that’s for sure.” They continued to eat, then they stopped when they were full.   
“so… movies. what shall we watch?”  
“I’ve got a few different movies…” They both went into the living area, and Gaster lead Sans over to the box of DVDs.   
“Some sci fi movies, some horror… I have a lot I’ve accumulated over the years.”  
“ummm… let’s watch this one.” It appeared to be a random movie about a mastermind creating a robot and trying to destroy the planet with it, and failing. The two skeletons decided to grab some snacks and grab some blankets, and they got comfortable on the couch, watching the movie.  
Most of the movie ended up being filled with Sans and Gaster laughing over the bad quality of it.   
“that was so funny!! let’s watch another one!”  
“Alright. Howabout this documentary on physics?”  
“sure. at least i won’t end up breaking my ribs in laughter over it.” They both chuckled, and they proceeded to watch the documentary. As It went on, Gaster was slowly but surely wrapping his right arm around Sans, slowly and surely pulling him closer. Sans noticed this, and he wrapped both of his arms around Gaster’s waist, leaning his head on the taller skeleton’s body. They both settled in this position, comfortable. Sans wasn’t even watching the documentary anymore, and he was looking up at Gaster instead. He knew that Gaster was focused on the documentary, but he decided to quietly talk.   
“you’re amazing, gaster.” He suddenly began to blush when he saw Gaster look down at him and smile, replying.   
“And so are you, Sans.” Sans hugged him tighter, burying his head into Gaster’s arm pit. He ended up falling asleep in this position, and Gaster didn’t dare move, not wanting to make Sans uncomfortable. He decided to keep the documentary going, and then he eventually hit the sack as well.

**Notes for the Chapter:**

> if you enjoyed this, please leave kudos and leave a comment!  
> please give me any tips you may have for me, I wanna get better at writing :^)
> 
> please check out my deviantart account btw! it's sawborg-pies


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